1. Field of the Invention
The present invention relates to an organic EL display panel using an organic electroluminescence element (hereinafter referred to as “organic EL element”) and a method of manufacturing the same, and relates in particular to a technique of improving a structure around an anode.
2. Description of the Related Art
The organic EL element is a current-drive type light-emitting element, and has a basic structure in which a light-emitting layer (including an organic light-emitting material) is positioned between an anode and a cathode. When an organic EL display panel in which organic EL elements are used is driven, voltage is applied between the anode and the cathode. A hole is injected from the anode and an electron is injected from the cathode. In this way, the hole and the electron are recombined in the light-emitting layer so as to cause an electroluminescence phenomenon. The organic light-emitting element takes advantage of this electroluminescence phenomenon. The organic EL element itself emits light and has an excellent visibility. Also, the organic EL element is a solid state component and has an excellent impact-resistance.
According to one of a method of forming a coated organic EL element, ink containing an appropriate amount of macromolecular material and an appropriate amount of low molecules having an excellent thin-film forming property is prepared and is applied on a substrate in an inkjet method or the like so as to form a light-emitting layer and a charge injection layer. There are organic EL display panels in each of which a plurality of coated organic EL elements are disposed in a matrix on the substrate having a TFT wiring part. In recent years, such organic EL display panels have been put to practical use as various types of displays and image display devices, for example.
On the substrate, the organic EL elements are partitioned by banks (barrier ribs) having a predetermined shape. In one of representative line bank structures, a plurality of line banks that extend in a column direction are parallel-arranged in a row direction. Light-emitting elements having the same color are arranged at a predetermined interval between adjacent banks. Light-emitting elements each having one of R, G and B colors are arranged in the row direction so as to perform a color display when a panel as whole is viewed.
FIG. 10 shows some of processes of manufacturing a conventional organic EL display panel. As shown in (e-3) of FIG. 10, an anode (lower electrode) 6X is disposed, in each element forming area, along a longitudinal direction of the bank 10 (an X direction). A gap 11 exists between adjacent element forming areas. The lower electrode 6 is an elongated electrode composed of a reflective metal film 60 and a transparent conductive film 61 layered thereon. The reflective metal film 60 is electrically connected to a power supply electrode 3 of the TFT wiring part through an opening (contact hole 8). Here, the contact hole 8 penetrates through a planarizing film 4. The contact hole 8 is usually formed in a vicinity of an end portion of the lower electrode 6 in the X direction in a non-luminescent area (pixel definition area) of the organic EL element instead of a light-emitting area of the organic EL element. As shown in FIG. 7, an (organic) light-emitting layer 7, an upper electrode 9 and a sealing layer (not depicted) are formed in this order on the lower electrode 6.
In each of the organic EL elements formed on the substrate, a thickness of the light-emitting layer 7 tends to be smaller around edge portions of the reflective metal film 60 in a vicinity of the gap 11 and around the contact hole 8 (especially around an edge of the opening), as shown in FIG. 7. Therefore, a short possibly occurs due to the light-emitting layer 7 being cut and an anomalous light emission possibly occurs due to electrical field concentration in a portion of the light-emitting layer 7 where the thickness is small.
Also, it is necessary that the organic EL elements that are adjacent to one another in the row direction (in the X direction) are defined and separated from one another so as to achieve an appropriate image display performance, in the organic EL display panel having the line bank structure. Therefore, the pixel definition layer 66 is provided between the transparent conductive film 61 and the light-emitting layer 7, as shown in FIG. 8 and (e-3) of FIG. 10. Here, the pixel definition layer 66 is formed using an insulating material such as SiON, and is formed to extend in a direction perpendicular to the longitudinal direction of the bank 10 (the X direction). In an area in which the pixel definition layer 66 is provided, it is possible to prevent current from flowing from the lower electrode 6 and the upper electrode 9 to the light-emitting layer 7 when the organic EL display panel is driven. Certain effects can be expected for preventing the short and uneven brightness due to the abnormal electrical field.
3. Patent Literatures    [Patent Literature 1] Japanese Patent Application Publication No. 2007-26754    [Patent Literature 2] Japanese Patent Application Publication No. 2007-59383